WDM ring network

ABSTRACT

A WDM ring network and method for distributing within such ring network for feeding in data and for distributing both working signals and protection signals on different transmission paths and in oppositely directed transmission directions, and for forwarding data from subscribers and for distributing the working signals to the subscribers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a WDM ring network, and method, whereinthe transmission capacity of such ring network, which is usedpredominantly for one-way data transport, can be taken advantage of.

2. Description of the Prior Art

In a ring network with predominantly one-way data transport, as in thecase of data transport within the Internet or in the case of videodistribution services, data is transmitted from a central networkelement, e.g. an internet server, toward the subscriber. In the case ofthe ring network utilization mentioned at the beginning, only verylimited data transport takes place from a subscriber to the centralnetwork element.

However, conventional transmission methods in the synchronous digitalhierarchy provide the same transmission capacity in the transmissiondirection both to and from the subscriber. Highly pronounced one-waydata transport entails the disadvantage that almost half of thetransmission capacity of the ring network remains unutilized.

The present invention is, therefore directed to a circuit arrangementand method with which the transmission capacity of a ring network withpredominantly one-way data transport can be used.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a ring network whichincludes: a central network element for feeding in data and fordistributing both working signals and protection signals on differenttransmission paths and in oppositely directed transmission directions,and wherein, proceeding from the central network element, the ringnetwork is subdivided into a first part and a second part; a pluralityof further network elements connected to subscribers for forwardingupstream data from the subscribers and for distributing the workingsignals to the subscribers; wherein the central network element feedsthe working signals into the first and second parts of the ring network;wherein the central network element, in accordance with portions of theworking signals fed into the first and second parts of the ring network,feeds the working signals as protection signals into the respectiveother part of the ring network; and wherein the further network elementsforward the protection signals as far as the respective network elementterminating the first and left-hand parts of the ring network, and theprotection signals are fed into the respective other terminating networkelement of the first and second parts of the ring network and areforwarded counter to a transmission direction of the working signals tothe central network element.

The present invention is further directed to a method for distributingdata within a ring network for feeding in data and for distributing bothworking signals and protection signals on different transmission pathsand in oppositely directed transmission directions and for forwardingdata from subscribers and for distributing the working signals to thesubscribers connected to network elements, the method including thesteps of: subdividing the ring network into a first part and a secondpart; feeding the working signals into both the first and second partsof the ring network; feeding the working signals as protection signalsinto a respective other part of the ring network; forwarding theprotection signals as far as the respective network element terminatingthe first and second parts of the ring network; feeding the protectionsignals into the respective other terminating network element of thefirst and second parts of the ring network; and forwarding theprotection signals counter to a transmission direction of the workingsignals to the central network element.

The present invention entails the advantage that the transmissioncapacity with predominantly one-way data transport on the ring networkis utilized, with transmission reliability remaining the same.

The present invention entails the advantage that data transport from thesubscriber to the central network element of the ring is also possible.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Preferred Embodiments and the Drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a construction and the data transport paths of aconventional ring network;

FIG. 2 shows a construction and the data transport paths of a ringnetwork according to the teachings of the present inventions;

FIG. 3 shows a configuration of a central network elements;

FIG. 4 shows a configuration of a network element,

FIG. 5 shows a configuration of network elements which respectivelyterminate one half of the ring network; and

FIG. 6 shows a further configuration of network elements whichrespectively terminate one half of the ring network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the synchronous digital hierarchy SDH, use is preferably made of ringstructures in which individual network elements for coupling out orcoupling in data are integrated. The ring structure enables thetransmission of data which, if they are transmitted directly to thesubscriber, are designated as working signals. Owing to the high degreeof data protection demanded, the data to be transmitted to thesubscriber is also transmitted as protection signals on a secondtransmission path within the ring to the subscriber. This type of datatransmission ensures a high degree of transmission reliability in theevent of an interruption of the ring.

The present invention's method with associated circuit configurationwill be explained in more detail using a ring structure with synchronoustransfer mode STM data transmission.

First of all, in order to provide a better understanding of the presentinvention, all data transport directed one-way will be assumed, in whichno data transport takes place from a subscriber to the central networkelement.

FIG. 1 illustrates a ring network which is known in the prior art. Inthis figure, a central network element A and a multiplicity of networkelements B to G are arranged in the ring. 16×STM-1 signals, e.g. from acentral internet server, are fed into the central network element A ofthe ring, in which the data is transmitted via a synchronous transfermode STM. In the central network element A, the data is fed into thering both in the clockwise direction as working signals W on a workingpath WW and in the counterclockwise direction as protection signals P ina protection path PW. The working path WW is represented by a solid lineand the protection path PW is represented by a broken line.

In the event of an interruption in the ring, e.g. between the networkelement C and the network element D, the network elements B and Ccontinue to be reached via the working path. The network elements D toG, in contrast, are supplied with the protection signals P.

The protection method used is a subnetwork connection protection SNCPmethod, also referred to as path protection method. This method issuitable, in particular, in the case of data traffic directed one-waysince it offers the same transmission capacity in the ring as a sharedring protection method. In this method, the control of the working andprotection signals is simple to achieve since there is no need for anychangeover protocols for a changeover in the network elements. Thechangeover in the network elements is, in each case, effected at thereceiving end on the basis of local information.

FIG. 2 illustrates the data paths within the ring according to thepresent invention. The working path WWR, WWL is represented by a solidline and the protection path PWR, PWL is represented by a broken line.In the case of the method of the present invention, the ring islogically subdivided into two ring halves, proceeding from the networkelement A. 32×STM-1 signals are fed into the ring by the central networkelement A, which also can be referred to as gateway node A. In thiscase, 16×STM-1 signals are fed into the ring as working signals WR onthe working path WWR in the clockwise direction and 16×STM-1 signals arefed into the ring as working signals WL on the working path WWL in thecounterclockwise direction. According to the method of the presentinvention, the protection signals PR, PL are transmitted on separatepaths from the central network node A to the terminating network elementpair D, E, between which the first and second parts of the ring adjoinone another. In the figure shown, the logical separating point of thering subdivided into two ring halves is between the terminating networkelements D and E. In the clockwise direction, data fed into the ring isforwarded in the left-hand ring half and, respectively, first part ofthe ring in the counterclockwise direction as protection signals pastthe network elements G and F as far as the network element E. Only inthe terminating network element E are the protection signals fed intothe ring and run in the opposite direction to the working signals in theright-hand ring half and, respectively, into the second part of the ringto the central network node A. The same procedure is effected with thedata fed into the left-hand ring half and, respectively, into the firstpart of the ring. In this case, the protection signals are fed past thenetwork elements B and C and selected only at the terminating networkelement D and fed into the terminating network element E into theright-hand ring half and run in the opposite transmission direction inthe left-hand ring half to the working signals transmitted in theleft-hand ring half.

A configuration of the central network node A is represented in FIG. 3.The core of the central network node A is formed by an add/dropmultiplexer A/D-MUX, to which 32×STM-1 signals are fed. The add/dropmultiplexer A/D-MUX is designed with a tributary connection T, aswitching matrix KF and optical STM-16 line interfaces East and West.The line A interfaces East and West output optical signals, formed, forexample, by selective lasers with specific wavelengths λ1 and λ2. Thereare arranged at the line interfaces East and West, in each case inseries, an optical splitter OSO, OSW and an optical filter OFO, OFW. Inthe optical splitter OSO, the optical signal λ1 is split into workingsignals λ1WL and into protection signals λ1PL. In the optical splitterOSW connected to the line interface West, the optical signal λ2 is splitinto working signals λ2WR and protection signals λPR.

Downstream of the line interface East, in the optical filter OFO, theworking signals λ1WL of the line interface East and the protectionsignals λ2PR formed in the optical splitter OSW at the line interfaceWest are added and form an optical signal λ1WL and λ2PR. An opticalsignal λ2WR and λ1PL is formed by the optical filter OFW in acorresponding manner in the opposite direction.

The working and protection signals λ1WL, λ2PR and λ2WR, λ1PL,respectively, are in each case forwarded to the nearest networkelenments G, F, E and B, C, D, respectively.

At both optical filters OFO, OFW, however, there is also the possibilityof selecting a desired optical signal.

Instead of the optical filters OFO, OFW, it is also possible to usewavelength division multiplexers WDM. Protection signals and upstreamsignals pass to the line interfaces East and West from the respectivelyfollowing network elements.

FIG. 4 shows a configuration of the network elements B, C, F and G ofthe ring. An optical filter OF or a wavelength division demultiplexerWDM/D; wavelength division multiplexer WDM/M in the network elements Fand G in the left-hand ring half taps off from the optical signal λ1WL,λ2PR the working signal λ1WL and allows the protection signal λ2PR topass. Likewise, the protection signal λ1PL in the optical filters OF ofthe network elements B, C in the right-hand ring half are fed past thenetwork elements B, C in the right-hand ring half.

At the line interface West, the working signal λ1WL is fed to theadd/drop multiplexer A/D-MUX, and through the switching matrix KF,signals intended for subscriber TL connected to this network element arecoupled out and passed on to the subscriber TL via a tributaryconnection T.

Portions of the working signal λ1WL that are to be forwarded are coupledvia the line interface East once again via the optical filter OF intothe data stream on the working path WWL of the ring, so that an opticalsignal λ1WL and λ2PR is once again produced. In the opposite direction,at the line interface East, in this case, the protection and upstreamsignals can be applied to the A/D MUX. In the right-hand half of thering, via same procedure, a specific signal for a subscriber in thenetwork elements B, C is coupled out, the remainder of the workingsignal is coupled in again and protection and upstream signals areforwarded.

FIG. 5 shows a configuration of the terminating network elements D and Ewhich respectively terminate one half of the ring network. With the aidof an optical filter OF or a wavelength division demultiplexer WDM/D,the working signal λ1WL is coupled out from the terminating networkelement E and fed to a line interface East of the terminating networkelement E. The protection signal λ2PR is fed, if appropriate, via anoptical amplifier OA to the line interface East of the terminatingnetwork element D. Via the switching matrix KF of the terminatingnetwork element D and the line interface West of the terminating networkelement D, the protection signals λ2PR previously forwarded on to theauxiliary protection path HPWR in the left-hand half of the ring passinto the protection path PWR of the right-hand half R of the ringnetwork RN. The protection signals λ1PL which were previously forwardedon the auxiliary protection path HPWL in the right-hand half R of thering network RN pass via the line interface West, the switching matrixKF and via the line interface East into the protection path PWL of theleft-hand half L of the ring network.

FIG. 6 shows a further configuration of the network elements D and Ewhich respectively terminate one half of the ring net work. Thisconfiguration differs from that shown in FIG. 5 by virtue of the factthat data is sent from a subscribers TL connected to these networkelements to other network elements or to the central network element Awithin the left-hand or right-hand half of the ring. In a departure fromthe illustration from FIG. 5, the protection signal λ2PR is fed from theoptical filter OF via a tributary connection to the switching matrix KFof the network element E. The protection upstream data transport islikewise fed in the switching matrix KF. Between the line interfacesEast of the network element D and the line interface West of the networkelement E, the aggregate signal formed from protection signal λ2PR andprotection upstream signal, and also the aggregate signal formed fromthe protection signal λ1PL and protection upstream signal, are output.The upstream data stream in the ring correspondingly reduces thecapacity of the data fed into the central network element A.

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the invention as set forth in the hereafter appended claims.

1. A ring network, comprising: a central network element for feeding indata and for distributing both working signals and protection signals ondifferent transmission paths and in oppositely directed transmissiondirections, and wherein, proceeding from the central network element,the ring network is subdivided into a first part and a second part; aplurality of further network elements connected to subscribers forforwarding upstream data from the subscribers and for distributing theworking signals to the subscribers; wherein the central network elementfeeds a respective working signals into the first and second parts ofthe ring network; wherein the central network element, in accordancewith portions of the respective working signals fed into the first andsecond parts of the ring network, feeds the working signals asprotection signals into the respective other part of the ring network;and wherein the further network elements forward the protection signalsas far as the respective network element terminating the first andleft-hand parts of the ring network, and the protection signals are fedinto the respective other terminating network element of the first andsecond parts of the ring network and are forwarded counter to atransmission direction of the working signals to the central networkelement.
 2. A ring network as claimed in claim 1, wherein the networkelements terminating the first and second parts of the ring network aredesigned such that the protection signals previously forward at thefurther network elements are selected and fed into the respective otherterminating network element of the first and second parts of the ringnetwork.
 3. A ring network as claimed in claim 1, further comprising:optical splitters for splitting the working signals.
 4. A ring networkas claimed in claim 1, further comprising: one of optical filters andmultiplexers for joining together different optical signals.
 5. A methodfor distributing data within a ring network for feeding in data and fordistributing both working signals and protection signals on differenttransmission paths and in oppositely directed transmission directionsand for forwarding data from subscribers and for distributing theworking signals to the subscribers connected to network elements, themethod comprising the steps of: subdividing the ring network into afirst part and a second part; feeding a working signals into the firstpart and a working signal into a second part of the ring network;feeding a working signal as a protection signal into each respectiveother part of the ring network in accordance with the respective workingsignals fed into the first and second parts of the ring network;forwarding the protection signals as far as the respective networkelement terminating the first and second parts of the ring network;feeding the protection signals into the respective other terminatingnetwork element of the first and second parts of the ring network; andforwarding the protection signals counter to a transmission direction ofthe working signals to the central network element.
 6. A method fordistributing data within a ring network as claimed in claim 5, themethod further comprising the steps of: selecting, in the terminatingnetwork elements, the protection signals forwarded at the furthernetwork elements; and feeding the protection signals into the respectiveother terminating network element of the first and second parts of thering.